Mechanisms for NH3 decomposition on Si(100)-(2 x 1) surface: A quantum chemical cluster model study
- 化学化工－已发表论文 
In this paper, we present a detailed mechanism for the complete decomposition of NH3 to NHx(a) (x= 0-2). Our calculations show that the initial decomposition of NH3 to NH2(a) and H(a) is facile, with a transition-state energy 7.4 kcal mol(-1) below the vacuum level. Further decomposition to N(a) or recombination-desorption to NH3(g) is hindered by a large barrier of similar to46 kcal mol(-1). There are two plausible NH2 decomposition pathways: 1) NH2(a) insertion into the surface Si-Si dimer bond, and 2) NH2(a) insertion into the Si-Si backbond. We find that pathway (1) leads to the formation of a surface Si=N unit, similar to a terminal Si=Nt pair in silicon nitride, Si3N4, while pathway (2) leads to the formation of a near-planar, subsurface Si3N unit, in analogy to a central nitrogen atom (N-c) bounded to three silicon atoms in the Si,N, environment. Based on these results, a plausible microscopic mechanism for the nitridation of the Si(100) - (2 x 1) surface by NH3 is proposed.